12 trigonometri

m(DBA)=b olsun
tanb=5/15=1/3
tan(a+b)=(tana+tanb)/(1- tana.tanb)=8/15
15tana+15tanb=8-8.tana.tanb
15tana+5=8-8tana/3
15tana+(8tana)/3=3
53tana /3=3
53tana=9
tana=9/53
CEVAP D